Support effect on the catalytic performance of Au/Co3O4–CeO2 catalysts for CO and CH4 oxidation

The Effect P Additive on the CeZrAl Support Properties and the Activity of the Pd Catalysts in Propane Oxidation

The properties of a catalyst support are closely related to the catalyst activity, yet the focus is often placed on the active species, with little attention given to the support properties. In this work, we specifically investigated the changes in support properties after the addition of P, as well as their impact on catalyst activity when used for catalyst preparation. We prepared the CeO2-ZrO2-P2O5-Al2O3 (CeZrPAl) composite oxides using the sol-gel, impregnation, and mechanical mixing methods, and characterized the support properties using techniques such as XRD, XPS, SEM-EDS, N2 adsorption-desorption, and Raman spectra. The results showed that the support prepared using the sol-gel method can exhibit a more stable phase structure, larger surface area, higher adsorption capacity for oxygen species, and greater oxygen storage capacity. The addition of an appropriate amount of P is necessary. On the one hand, the crystallization and growth of CePO4 can lead to a decrease in the Ce content in the cubic phase ceria-zirconia solid solution, resulting in a phase separation of the ceria-zirconia solid solution. On the other hand, CePO4 can lock some of the Ce3+/Ce4+ redox pairs, leading to a reduction in the adsorption of oxygen species and a decrease in the oxygen storage capacity of the CeZrPAl composite oxides. The research results indicated that the optimal P addition is 6 wt.% in the support. Therefore, we prepared a Pd/CeZrPAl catalyst using CeZrAl with 6 wt.% P2O5 as the support and conducted the catalytic oxidation of C3H8. Compared with the support without P added, the catalyst activity of the support loaded with P was significantly improved. The fresh and aged (1000 °C/5 h) catalysts decreased by 20 °C and 5 °C in T50 (C3H8 conversion temperature of 50%), and by 81 °C and 15 °C in T90 (C3H8 conversion temperature of 90%), respectively.

Strong metal support interaction (SMSI) and MoO3 synergistic effect of Pt-based catalysts on the promotion of CO activity and sulfur resistance

In industrial applications, Pt-based catalysts for CO oxidation have the dual challenges of CO self-poisoning and SO2 toxicity. This study used synthetic Keggin-type H3PMo12O40 (PMA) as the site of Pt, and the Pt-MoO3 produced by decomposition of PMA was anchored to TiO2 to construct the dual-interface structure of Pt-MoO3 and Pt-TiO2, abbreviated as Pt-P&M/TiO2. Pt-0.125P&M/TiO2 with a molar ratio of Pt to PMA of 8:1 showed both good CO oxidation activity and SO2 tolerance. In the CO activity test, the CO complete conversion temperature T100 of Pt-0.125P&M/TiO2 was 113 ℃ (compared with 135 ℃ for Pt/TiO2). In the SO2 resistance test, the conversion efficiency of Pt-0.125P&M/TiO2 at 170 ℃ remained at 60% after 72 h, while that of Pt/TiO2 was only 13%. H2-TPR and XPS tests revealed that lattice oxygen provided by TiO2 and hydroxyl produced by MoO3 increased the CO reaction rate on Pt. According to the DFT theoretical calculation, the electronegative MoO3 attracted the d-orbital electrons of Pt, which reduced the adsorption energy of CO and SO2 from - 4.15 eV and - 2.54 eV to - 3.56 eV and - 1.52 eV, respectively, and further weakened the influence of strong CO adsorption and SO2 poisoning on the catalyst. This work explored the relationship between catalyst structure and catalyst performance and provided a feasible technical idea for the design of high-performance CO catalysts in industrial applications.

Three dimensional nickel foam carried sea urchin-like copper-cobalt-cerium cathode for enhanced tetracycline wastewater purification in photocatalytic fuel cell

Photocatalytic fuel cells (PFCs) regarded as a potential sustainable technique, have been broadly reported. In this work, the carbon quantum dot-loaded TiO2 photoanode and sea urchin-like CuCoCe ternary metal oxide cathode materials are successfully synthesized and used to construct PFC systems for efficient tetracycline (TC) degradation (45 mg/L) and simultaneous electricity generation. The results demonstrate that the CQDs-modified TiO2 photoanode has improved absorption intensity in both the UV and visible regions, and the photocurrent density at 1.23 V vs RHE reached 1.31 mA cm-2, which is 1.3 times higher than that of the original TiO2 photoanode. The established PFC system achieves the highest removal ratio of 96.9 % for TC in 60 min with a maximum power density of 0.77 mW cm-2. The PFC system can operate efficiently over a wide pH range (3.0-9.0). Furthermore, quenching experiments and ESR spectra show that the main reactive oxygen species in the degradation process are •O2-, 1O2 and •OH. This study provides meaningful way to develop multiple metal oxides as cathode of PFC system for efficient organic pollutant degradation and energy recovery.

Recent Advances in Co3O4-Based Composites: Synthesis and Application in Combustion of Methane

In recent years, it has been found that adjusting the organizational structure of Co₃O₄ through solid solution and other methods can effectively improve its catalytic performance for the oxidation of low concentration methane. Its catalytic activity is close to that of metal Pd, which is expected to replace costly noble metal catalysts. Therefore, the in-depth research on the mechanism and methods of Co₃O₄ microstructure regulation has very important academic value and economic benefits. In this paper, we reviewed the catalytic oxidation mechanism, microstructure regulation mechanism, and methods of nano-Co₃O₄ on methane gas, which provides reference for the development of high-activity Co₃O₄-based methane combustion catalysts. Through literature investigation, it is found that the surface energy state of nano-Co₃O₄ can be adjusted by loading of noble metals, resulting in the reduction of Co-O bond strength, thus accelerating the formation of reactive oxygen species chemical bonds, and improving its catalytic effect. Secondly, the use of metal oxides and non-metallic oxide carriers helps to disperse and stabilize cobalt ions, improve the structural elasticity of Co₃O₄, and ultimately improve its catalytic performance. In addition, the performance of the catalyst can be improved by adjusting the microstructure of the composite catalyst and optimizing the preparation process. In this review, we summarize the catalytic mechanism and microstructure regulation of nano-Co₃O₄ and its composite catalysts (embedded with noble metals or combined with metallic and nonmetallic oxides) for methane combustion. Notably, this review delves into the substance of measures that can be used to improve the catalytic performance of Co₃O₄, highlighting the constructive role of components in composite catalysts that can improve the catalytic capacity of Co₃O₄. Firstly, the research status of Co₃O₄ composite catalyst is reviewed in this paper. It is hoped that relevant researchers can get inspiration from this paper and develop high-activity Co₃O₄-based methane combustion catalyst.

Unraveling Nanoscale Cobalt Oxide Catalysts for the Oxygen Evolution Reaction: Maximum Performance, Minimum Effort

The oxygen evolution reaction (OER) is a key bottleneck step of artificial photosynthesis and an essential topic in renewable energy research. Therefore, stable, efficient, and economical water oxidation catalysts (WOCs) are in high demand and cobalt-based nanomaterials are promising targets. Herein, we tackle two key open questions after decades of research into cobalt-assisted visible-light-driven water oxidation: What makes simple cobalt-based precipitates so highly active-and to what extent do we need Co-WOC design? Hence, we started from Co(NO₃)₂ to generate a precursor precipitate, which transforms into a highly active WOC during the photocatalytic process with a [Ru(bpy)₃]²⁺/S₂O₈^2-/borate buffer standard assay that outperforms state of the art cobalt catalysts. The structural transformations of these nanosized Co catalysts were monitored with a wide range of characterization techniques. The results reveal that the precipitated catalyst does not fully change into an amorphous CoO_x material but develops some crystalline features. The transition from the precipitate into a disordered Co₃O₄ material proceeds within ca. 1 min, followed by further transformation into highly active disordered CoOOH within the first 10 min. Furthermore, under noncatalytic conditions, the precursor directly transforms into CoOOH. Moreover, fast precipitation and isolation afford a highly active precatalyst with an exceptional O₂ yield of 91% for water oxidation with the visible-light-driven [Ru(bpy)₃]²⁺/S₂O₈^2- assay, which outperforms a wide range of carefully designed Co-containing WOCs. We thus demonstrate that high-performance cobalt-based OER catalysts indeed emerge effortlessly from a self-optimization process favoring the formation of Co(III) centers in all-octahedral environments. This paves the way to new low-maintenance flow chemistry OER processes.

Promoting Effect of Palladium on ZnAl2O4-Supported Catalysts Based on Cobalt or Copper Oxide on the Activity for the Total Propene Oxidation

Palladium-modified Co-ZnAland Cu-ZnAl materials were used and found active for the catalytic oxidation of propene and propane. According to the results obtained by XRD, TPR and XPS, the zinc aluminate-supported phases are oxide phases, Co₃O₄, CuO and PdO_x for Co-ZnAl, Cu-ZnAl and Pd-ZnAl catalysts, respectively. These reducible oxide species present good catalytic activity for the oxidation reactions. The addition of palladium to Co-ZnAl or Cu-ZnAl samples promoted the reducibility of the system and, consequently, produced a synergic effect which enhanced the activity for the propene oxidation. The PdCo-ZnAl sample was the most active and exhibited highly dispersed PdO_x particles and surface structural defects. In addition, it exhibited good catalytic stability. The H₂ pre-treated PdCu-ZnAl, PdCo-ZnAl and Pd-ZnAl samples showed higher activity than the original oxide catalysts, evidencing the important role of the oxidation state of the species, mainly of the palladium species, on the catalytic activity for the propene combustion. The synergic effect between metal transition oxides and PdO_x could not be observed for the propane oxidation.

A catalyst powder-based spraying approach for rapid and efficient removal of fire-generated CO：From laboratory to pilot scale

In confined space fires, the large amount of CO generated by incomplete combustion of carbon-based materials poses a serious threat to the trapped people. However, the efficient method of removing CO in such disasters remains a great challenge. Herein, a spraying catalyst powder (SCP) approach is proposed for CO removal by oxidizing CO to harmless CO₂. Cu/Mn catalyst, synthesized by using ethylene glycol as solvent, was employed in this study. The influence of catalyst concentration, temperature, CO₂ concentration and initial CO concentration on CO removal performance of SCP approach was investigated. With 500 g/m³ catalyst, 25,000 ppm CO could be reduced to 2550 ppm within 1 min and completely removed in less than 2.83 min at 200 °C. The feasibility of SCP approach in practical application was validated by the remarkable CO removal performance for charcoal combustion in confined tunnel. SCP approach could effectively reduce the CO concentration, which would reach up to 12,659 ppm in the absence of SCP approach, to less than 1500 ppm within 30 min. The experiment results suggest that SCP technology can effectively remove the fire-generated CO and is promising for practical application in crowded occupancies, such as underground space and aircraft compartment.

Current scenario of CNG vehicular pollution and their possible abatement technologies: an overview

Compressed natural gas is an alternative green fuel for automobile industry. Recently, the Indian government is targeting to replace all the conventional fuel vehicles by compressed natural gas (CNG) automobiles due to its several merits. Still, the presence of a significant amount of CO, CH₄, and NO_x gases in the CNG vehicle exhaust are quiet a matter of concern. Thus, to control the emissions from CNG engines, the major advances are under development of and oxidation is one of them in catalytic converter. In literature, the catalysts such as noble and non-noble metals have been reported for separate oxidation of CO and CH_4.. Experimentally, it was found that non-noble metal catalysts are preferred due to its low cost, good thermal stability, and molding tractability. In literature, several articles have been published for CO and CH₄ oxidation but no review paper is still available. Thus, the present review provides a comprehensive overview of separate as well as simultaneous CO and CH₄ oxidation reactions for CNG vehicular emission control.

Rod-Like Nanoporous CeO2 Modified by PdO Nanoparticles for CO Oxidation and Methane Combustion with High Catalytic Activity and Water Resistance

A PdO/CeO2 composite with a rod-like nanoporous skeletal structure was prepared by combining the dealloying of Al-Ce-Pd alloy ribbons with calcination. For CO oxidation and CH4 combustion, the nanoporous PdO/CeO2 composite exhibits excellent catalytic activity, and the complete reaction temperatures of CO and CH4 are 80 °C and 380 °C, respectively. In addition, the composite possesses excellent cycle stability, CO2 toxicity, and water resistance, and the catalytic activity hardly decreases after 100 h of long-term stability testing in the presence of water vapour (2 × 105 ppm). The results of a series of characterizations indicate that the enhanced catalytic activity can be attributed to the good dispersion of the PdO nanoparticles, large specific surface area, strong redox capacity, interaction between PdO and CeO2, and more surface active oxygen on PdO. The results of the characterization and experiments also indicate that the PdO nanoparticles, prepared by combining dealloying and calcination, have a stronger catalytic activity than do Pd nanoparticles. Finally, a simple model is used to summarize the catalytic mechanism of the PdO/CeO2 composite. It is hoped that this work will provide insights into the development of high-activity catalysts.

Correction: Au@PdOx with a PdOx-rich shell and Au-rich core embedded in Co3O4 nanorods for catalytic combustion of methane

Correction for 'Au@PdO_x with a PdO_x-rich shell and Au-rich core embedded in Co₃O₄ nanorods for catalytic combustion of methane' by Yan Zhu et al., Nanoscale, 2017, 9, 2123-2128.

Highly dispersed CoOx in layered double oxides for oxidative dehydrogenation of propane: guest–host interactions

The host–guest interactions of layer-structured materials improved the dispersion of the active sites and tuned their reactivity toward ODHP reaction.

Deoxygenation of coal bed methane on LaCoO3 perovskite catalyst: the structure evolution and catalytic performance

Deoxygenation of coal bed methane: the structure evolution and activation of a LaCoO₃ perovskite catalyst.

Variation of redox activity and synergistic effect for improving the preferential oxidation of CO in H2-rich gases in porous Pt/CeO2–Co3O4 catalysts

The porous Pt/CeO₂–Co₃O₄ catalysts show superior catalytic performance for CO preferential oxidation in H₂-rich gases.

The Influence of Deposition Methods of Support Layer on Cordierite Substrate on the Characteristics of a MnO₂-NiO-Co₃O₄/Ce0.2Zr0.8O₂/Cordierite Three Way Catalyst

This paper compares different coating methods (in situ solid combustion, hybrid deposition, secondary growth on seed, suspension, double deposition of wet impregnation and suspension) to deposit Ce_0.2Zr_0.8O₂ mixed oxides on cordierite substrates, for use as a three way catalyst. Among them, the double deposition was proven to be the most efficient one. The coated sample shows a BET (Brunauer-Emmett-Teller) surface area of 25 m²/g, combined with a dense and crack free surface. The catalyst with a layer of MnO₂-NiO-Co₃O₄ mixed oxides on top of the Ce_0.2Zr_0.8O₂/cordierite substrate prepared by this method exhibits good activity for the treatment of CO, NO and C₃H₆ in exhaust gases (CO conversion of 100% at 250 °C, C₃H₆ conversion of 100% at 400 °C and NO conversion of 40% at 400 °C).

Effect of CeO2 and Al2O3 on the activity of Pd/Co3O4/cordierite catalyst in the three-way catalysis reactions (CO/NO/CnHm)

The present article studies the effect of CeO2 and Al2O3 on the activity of Pd/Co3O4/cordierite catalyst in conversion of NO, CO, CnHm. The catalysts were characterized by temperature programmed reduction with hydrogen, X-ray diffraction, X-ray photoelectron spectroscopy and transmission electron microscopy. It is shown that the effect of CeO2 on the properties of Pd/Co3O4/cordierite catalyst depends on preparation method. The catalyst obtained by co-deposition of cerium and cobalt oxides has higher activity in CO oxidation (CO + O2 and CO + NO) and total hexane oxidation (C6H14 + O2). Such phenomenon is probably caused by more than stoichiometric amount of formed oxygen vacancies, an increase in both mobility of surface oxygen and dispersity of components in the catalytic composition. It is demonstrated that CeO2 addition promotes the SO2 resistance of Pd/Co3O4/cordierite. The second support decreases the activity of Pd/Co3O4/cordierite catalyst in the reactions of CO and C6H14 with oxygen because of CoAl2O4 formation.